Currently, dental restorations may be made by sintering metal powders. Metal powders are usually mixed with a binder to assist in the shaping or injection molding of the restorations. These restorations are made in larger dimensions to accommodate shrinkage that occurs during the sintering process. The binder may be present in an amount of up to about twenty percent with the remainder of the mixture being the powder. Restorations made from the binder/powder mixture undergo a binder removal step that occurs in the preheating stage, followed by sintering at a suitable temperature and in a suitable atmosphere in conventional heating ovens. These steps require long processing times and impose poor control on dimensional tolerance.
It has been found that microwave sintering has been effective in the manufacture of machine parts such as drill bit inserts, as set forth in U.S. Pat. No. 6,066,290. The patent discloses drill bit inserts manufactured from tungsten carbide and cobalt. Sintering by microwave is accomplished in a short period of time leaving the integrity of the alloy unchanged. U.S. Pat. No. 6,004,505 is directed to a process and apparatus for the preparation of particulate or solid parts. Hard wear parts are made from tungsten carbide or silicon nitride particles that are packed into a mold or cavity and sintered in a microwave sintering apparatus. U.S. Pat. No. 5,808,282 discloses a microwave sintering process for ceramics, ceramic composites, and metal materials. The process involves surrounding the material with a granular susceptor bed, flowing a protective gas around the material, and irradiating the material and bed with microwave energy. The patent is directed to the sintering of cutting tools. None of the prior art address the sintering of certain powder metals used in the manufacture of dental restorations.
It is beneficial to reduce the processing and sintering time required in the manufacture dental restorations. It is desirable to be able to better control the properties of dental restorations during manufacture thereof.